Roman Numeral Converter

Roman Numeral Converter is a browser-based utility for instant bidirectional conversion between Arabic numbers (1-3999) and Roman numerals (I-MMMCMXCIX). Type an Arabic number to see its Roman numeral equivalent in real time, or enter a Roman numeral to get the corresponding Arabic number.

This tool fully supports the subtractive notation rules that form the foundation of Roman numeral notation. In subtractive notation, I is placed before V or X to represent 4 (IV) and 9 (IX). Similarly, X is placed before L or C to represent 40 (XL) and 90 (XC), and C is placed before D or M to represent 400 (CD) and 900 (CM). The converter automatically validates these rules and detects any malformed notation, immediately flagging invalid entries.

Roman numerals are useful in many contexts: studying history, reading clock faces, decoding production years on films and television shows, interpreting dates carved into buildings and monuments, solving programming exercises, and creating school assignments or quizzes. A curated list of common Roman numeral examples is displayed for quick reference, making this an ideal educational resource for learning how Roman numeral notation works.

All processing runs entirely in your browser with no data ever sent to a server. No installation or account registration is required.